I recently installed LP-PAN2 band scope, which is fantastic. In the past have played, briefly, with a few band scopes/spectrum scopes, but nothing anywhere near as sensitive or effective as this one, at least for the HF band. I find myself enthralled now with being able to visualize the many strange forms of radio emissions on the HF band. And their is more interesting and weird stuff than I ever imagined when all I could do was hear one 3kHz to 6kHz bandwidth at a time.

I am realistic enough to expect that much of it is stuff that civilians will never get understanding of, but is there any web site that catalogues or discusses the known and the unknown?

"I am realistic enough to expect that much of it is stuff that civilians will never get understanding of, but is there any web site that catalogues or discusses the known and the unknown?"

If I understand your question right, you are wondering what different forms of modulation & signal types you might find on HF? I'm not positive of your question.....but, Google is your friend. Just for starts see these two sites below. In addition there were hundreds of others I found in just a few minutes.

I know those two sites, somewhat. The emissions I am asking about are not found in the amateur band, and are not listed on those sites. But I will look at the yahoo "HFMonitors" yahoo group, which in linked on the HF-Digital Decoding page and which I didn't notice before. That looks like a good place to start, and may be close to what I was hoping to find. Thanks.

Maybe you can give us a freq of some of the signals that are stumping you and a description of what you heard. Between those two sites I see the vast majority of schemes identified so if it is something different that would be neat to hear.

Maybe you can give us a freq of some of the signals that are stumping you and a description of what you heard. Between those two sites I see the vast majority of schemes identified so if it is something different that would be neat to hear.

W8BYA

Thanks. I'm not the most computer capable person, by any means. I will see if I can figure out a way to record the screen video of the emission waveforms, and the audio, for some of the strange ones, and post it here. That is kind of what I was hoping to find someone else has done. (I've seen a couple posted on You Tube.) But given my level of such computer skill, it might take a while.

I will describe one of the more simple emissions now. I'm sure you have heard what sounds like some delinquent ham sweeping a carrier up the ham bands, once in a while. However, watching the HF bands on a spectrum display, one can often see that kind of carrier sweep continuously through MANY mHz of spectrum, quite regularly. Often times it appears as a lower-level signal that one would never hear if your RX is tuned to another station. It is clear that this isn't some amateur or CB-er making mischief. I have tried to follow that carrier up the spectrum with my RX several times, but it is hard to manually match the tuning rate. It appears to be simply un-modulated carrier.

One of my speculations is that this is a signal transmitted by some military or government agency to allow distant operatives to pick a frequency that will most surely allow clandestine signals to reach home. For example, if you are an operative in Zimbabwe at 0700 local time, and want to make a coded transmission to a receiving station in Beijing, how can you choose the transmission frequency that best serves that path at that moment? Well, instead of taking a chance on time and frequency schedules that are picked for their normally expected reliability over that path, if you have the synchronized receiver that follows the swept transmitted carrier (originating near Beijing) up through the HF band from 5 mHz to 30 mHz, it would be easy to note the signal peaks. You would choose to make your coded transmission on one of those peaked signal frequencies. The Beijing-based operative in Cairo could use the same swept carrier signal for the same reason, at the same time. This would also allow the operative to make the transmission at the safest time, and not a pre-scheduled time. It could also help assure reliable communications with a very low-power transmitter.

But then the variable of antenna take-off angle might rather fatally complicate any such scheme.

I rather doubt if such a scheme would be used by any first-world government, with ready access to secure satellite communications, unless there might be a high cost to getting caught with the more sophisticated equipment.

Of course, this is all my speculation. I could be wildly wrong and maybe there is a well-known explanation for this swept carrier. Maybe I only revealing my ignorance here.

As I said, this is about the simplest of the many strange transmissions that are much easier to appreciate with a spectrum analyzer. I hope it explains my comment that us civilians are likely to never know the truth about most of it.

Another potential explanation that I came across in a search of message forum archives on "HFMonitors" is something called "Passive Ionospheric Sounding", but the parameters of this emission mode are not yet clear to me.

Somebody suggested that such signals could be a new form of digital over the horizon radar. This was suggested in the Eham Propagation forum. OTH radar is useful for detecting such things as missile launches. Many of us remember the Soviet Woodpecker that was a OTH radar system meant to keep an eye on America. It's possible that the USA has deployed an advanced OTH radar system as part of what's sometimes called Iron Dome or Star Wars, namely the missile interception system we all know about. It would make sense that to intercept a missile, we would have to detect it first, and that's where OTH radar comes in. OTH radar tends to emit signals on the HF spectrum, and it's possible that American military engineers have found a way to make it less obtrusive than the old woodpecker which got into landline telephones and various other stuff.

I have seen these signals go up and down in frequency on my HP SA. Have no idea what they are but the first thing that came to my mind was that someone modified their rig to xmt on all frequencies and was then tuning their VFO up and down in frequency checking the SWR of an antenna.

I believe the upward swept sounds are frequency sounders , probably government. In the late 80's the navy introduced 'chirp sounders' for propagation measurement, but I haven't heard them in years. They were quite intrusive and worked in discrete steps.

Do keep in mind that there are about a dozen ionospheric sounder sites around the world run by various governments or university research arms. You can find them on the web, with daily reports. The one at the HAARP site in Alaska is probably the most familiar.

Do keep in mind that there are about a dozen ionospheric sounder sites around the world run by various governments or university research arms. You can find them on the web, with daily reports. The one at the HAARP site in Alaska is probably the most familiar.

Can you post links to those web sites? I haven't found them.Can you provide a link to any site that describes sounders that sweep through the HF band, especially the upper half, which is where I most often see it?

Maybe we don't have complete information, but I cannot find any mention of HAARP transmissions that sweep in frequency at all, or above 10mHz in the HF band.. Here is the only thing I have found about HAARP transmission in the HF band:"The IRI can transmit between 2.7 and 10 MHz, a frequency range that lies above the AM radio broadcast band and well below Citizens' Band frequency allocations. The HAARP Station is licensed to transmit only in certain segments of this frequency range, however. When the IRI is transmitting, the bandwidth of the transmitted signal is 100 kHz or less. The IRI can transmit in continuous waves (CW) or in pulses as short as 10 microseconds (µs). CW transmission is generally used for ionospheric modification, while transmission in short pulses frequently repeated is used as a radar system. Researchers can run experiments that use both modes of transmission, first modifying the ionosphere for a predetermined amount of time, then measuring the decay of modification effects with pulsed transmissions."

I believe the upward swept sounds are frequency sounders , probably government. In the late 80's the navy introduced 'chirp sounders' for propagation measurement, but I haven't heard them in years. They were quite intrusive and worked in discrete steps.

Do keep in mind that there are about a dozen ionospheric sounder sites around the world run by various governments or university research arms. You can find them on the web, with daily reports. The one at the HAARP site in Alaska is probably the most familiar.

There are still chirp sounders, but this signal is different from them. It might be a new version of the same sort of system, though.

I have noted this signal many times, it seems to be fairly low power as another person mentioned.

I have also noticed a signal that is extremely broadband, which looks like a TV carrier but it sweeps really, really slowly - like one cycle per minute over several MHz. I should have taken a screenshot of it!

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